Water Journal : Water Journal November 2012-1
refereed paper odour management water NOVEMBER 2012 55 of a 1.5m-high packed bed of wood chips. The bio-bed was aerated from below, through a perforated floor. It was found that the EMTP odour complaints were the direct result of the changing inlet conditions of the biofilter. Biofilters adapt to certain limited inlet concentrations and hence by their nature are not necessarily very flexible in regard to changing odour types and concentrations. Different organic sludge cause different odours and the slow- reacting biofilter was not able to adapt to these changing conditions within short periods of time; in fact, frequent odour breakthroughs occurred, especially in winter-time. A decision was made to upgrade the odour treatment facility. Technology of Photoionisation Photoionisation is a “design-name” for a process that is essentially based on the application of UV light in combination with a catalyst. In contrast to conventional odour control (either biological or chemical), Photoionisation is a physical-chemical treatment method. It is sometimes misunderstood and considered to be another “ionisation technology”, but it actually describes a completely different technology. “Air-ionisation”, the conventional meaning, is used in households and commercial buildings with equipment located inside rooms or indirectly installed in ventilation systems to enrich the air with free oxygen ions. The ions are usually generated by corona-discharge technologies. Corona discharge describes the discharge process between two electrodes, which are separated by a dielectric barrier. Around the electrodes positively and negatively charged ions are formed, while the generation of ozone is typically suppressed. The technology of air-ionisation may be applied effectively for reduction of low concentrated odours and, besides odour reduction, may also kill micro-organisms. However, this technology is not suitable for treatment of highly concentrated odours such as those from wastewater treatment plants. As mentioned previously, “Photo- ionisation” is a process that is essentially based on the application of UV light and catalysts. It is an “ionisation” process, but besides the generation of ions, strong oxidants such as hydroxyl- radicals and ozone are also generated. Furthermore, under the radiation of UV light, Photoionisation breaks up odour components such as long-chain hydrocarbons to make them available for further oxidation. The catalysts work on the one hand by irradiation by UV light, and on the other by providing a surface to allow oxidation processes to take place. Additionally, the catalyst also has a “buffer” function that allows for effective treatment of peak odour concentrations (spikes). Photoionisation is especially suitable for treatment of highly concentrated odours and has gained a very positive reputation all over the world. The process was developed in Germany and was first mentioned in a newspaper in 2003 (Münchner Merkur, 2003). In the US, the technology was first mentioned in 2005 and 2007, and in Great Britain in 2006. The first installation in Australia was described by Little in 2010. Practical Importance of Photoionisation The technology of Photoionisation has gained a positive reputation all over the world with installations found in Europe, North America, Asia, Middle East and Australia. In contrast to conventional odour control, Photoionisation is essentially characterised by its high treatment efficiency, reliable operation and low maintenance demand. Only electricity is required for operation, with no other special operational conditions needed. While temperature and humidity are of importance for biological filtration systems, such environmental conditions do not affect Photoionisation. These facts allow for reliable operation. Maintenance demand is reduced to approximately one day per unit per year. The technology completely relinquishes complicated controls including sensors, dosing systems, etc, and has been described as an ideal odour control method for remote sewage pumping stations (Augustin, 2011). Photoionisation provides the following essential advantages: Figure 2. Humidifier, EMTP. Figure 1. Empty biofilter with perforated floor, EMTP. Figure 3. PI unit at one of the tanks, EMTP.
Water Journal December 2012
Water Journal September 2012-1